Re: [patch V3 05/12] rseq: Add prctl() to enable time slice extensions

[Thomas Gleixner <tglx@linutronix.de>]

On Fri, Oct 31 2025 at 15:43, Mathieu Desnoyers wrote:
> On 2025-10-29 09:22, Thomas Gleixner wrote:
>> +	case PR_RSEQ_SLICE_EXTENSION_SET: {
>> +		u32 rflags, valid = RSEQ_CS_FLAG_SLICE_EXT_AVAILABLE;
>> +		bool enable = !!(arg3 & PR_RSEQ_SLICE_EXT_ENABLE);
>> +
>> +		if (arg3 & ~PR_RSEQ_SLICE_EXT_ENABLE)
>> +			return -EINVAL;
>> +		if (!rseq_slice_extension_enabled())
>> +			return -ENOTSUPP;
>> +		if (!current->rseq.usrptr)
>> +			return -ENXIO;
>> +
>
> So what happens if we have an (unlikely) scenario of:
>
> - thread startup
> - thread registration to rseq
> - prctl PR_RSEQ_SLICE_EXTENSION_SET
> - rseq unregistration
> - rseq registration
> --> What's the status of slice extension here ?

On unregister it's cleared and you have to re-register it when you
register a new rseq. It's part of the rseq state so obviously it's all
set back to zero.